Matrix mat for plastic printing plate



United States Patent 3,318,240 MATRIX MAT FOR PLASTIC PRINTING PLATEWinfred Doyle Boggess, Indianapolis, Ind., assignor to The BeveridgePaper Company, Indianapolis, Ind., a corporation of Indiana No Drawing.Filed Feb. 21, 1966, Ser. No. 528,806 5 Claims. (Cl. 101401.2)

The present invention relates to a process of preparing a stereotypematrix mat for use in the preparation of plastic printing plates andfurther relates to the matrix mat having improved surf-ace propertieswhen prepared by said process. This invention is based in part on thesubject matter disclosed in Ser. No. 355,098, filed Mar. 26, 1964, andnow abandoned.

It is standard practice in the newspaper publishing industry to printnewspapers from metal printing plates formed of lead alloy. However,relatively recently it has been found that improved printing plates canbe manufactured using thermoplastic resins in place of lead alloy. Suchthermoplastic resin printing plates are more desirable than the leadalloy plates because of the lighter weight of the plastic and thesharper definition in printed word and illustration that can be achievedwith plastic.

In general, the above mentioned lead alloy plates are conventionallycast by the use of stereotype mats each of which consist of a relativelythick sheet of felted cellulose fibers which may be composed of ragstock, cotton linters, wood fibers produced by chemical pulpingprocesses, or the like. The stereotype mat itself is usually prepared byforming an aqueous slurry of the fibers in the wet machine or a papermaking machine. The slurry is felted out in the form of a web on thescreen of the wet machine and the Web is wound until a multiplicity oflayers has been built up to form a sheet or mat of the desiredthickness. for example, powdered clay, silicate or talc, is mixed withthe fibers in the wet machine and is, therefore, incorporated with thefibers in the body of the final sheet or mat.

The resulting sheet is then removed from the roll and is dried andcompressed to a thickness suitable for a stereotype mat, usually in therange of .026 to .070 inch. As the compressing operation is in process,the surface of the mat, which is to receive the impression and againstwhich the printing plate is to be cast, is calendered in order toprovide a dense smooth surface with as few projecting fibers aspossible. In contrast, the opposite surface of the mat is made porous byretaining said opposite surface against a porous uneven surface such asa woven fabric belt. In this manner, the opposite surface of the matbecomes porous and irregular and easily permits the passage of moisture.The impression-receiving surface of the mat is herein called the faceand the opposite surface is herein called the back.

After a matrix mat has been manufactured according to the above process,it has a certain amount of moisture therein depending in part upon therequirements of the customer. If the customer or newspaper plant isdesirous of using a stereotype mat having high shrinkage properties, themat may contain moisture as high as 35% by weight. On the other hand, iflow shrinkage properties are desired, for example, in the situation ofmulti-colored printing wherein the various colors must register with oneanother, the moisture content of the mat may be relatively low such as,for example, 12% by weight. At any rate, in its moistened, and thusplastic condition, the stereotype mat is pressed down against the formor pattern which may be an assembly of linotype characters,electrotypes, etc. arranged in the desired final configuration of theprinted newspaper page. The relatively damp matrix mat is then formedinto a semi-circular shape by mounting Usually, a filler such as,

3,318,240 Patented May 9, 1967 upon a semi-circular element and ishardened and dried out in the shape by the application of drying heatthereto in an apparatus known as a scorcher.

It is important that the moisture escape rapidly from the matrix withoutthe matrix rupturing by reason of the formation of steam within the mat.Because the back of the mat is relatively porous and irregular asdescribed above, the moisture can readily escape from the back so thatno rupturing occurs.

After the mat has been dried and hardened in the relatively rigidcondition as above described, the face containing the impression isadapted to impart an accurate reproduction to the printing plate whichis cast against the mat. conventionally, the reproduction is made bycasting the molten alloy metal against the face of the mat in a castingbox and subsequently allowing the metal to cool and solidify. Asmentioned, the dry mat is curved to a semi-circular shape in order toform the printing plate in a similarly curved shape for the reason thatmost printing is done by means of cylindrical presses.

It has been found that when an attempt is made to prepare athermoplastic resin casting by using said resin in place of lead alloyin the above described process employing a stereotype matrix, the resinflows into the pores of the mat on the face thereof even though the faceis dense and smooth and even though there are no visible projectingfibers. Consequently, after the resin printing plate has hardened, it isalways difiicult and frequently impossible, to separate the printingplate from the paper matrix. In the process of separating the plates theloose fibers are picked out and show up on the finished plate as well ason plates which are subsequently made from the same matrix mat. For theabove reasons, an important object of the present invention is toprovide a process of preparing a stereotype mat having good releaseproperties for use in the preparation of resin printing plates.

Another object of the invention is to provide an improved stereotype matwhich has good release properties when used with a resin plate.

Still another object of this invention is the preparing of an improvedstereotype mat whereby the release characteristics of the mat areenhanced by plasticizing in a proper manner the polyvinyl alcohol resinwith an appropriate plasticizer in order to intimately surround thesurface fibers in the face of the mat with the resin to prevent thesefrom being picked out and thus giving, for example, poor half toneimages. Moreover, another aspect of this invention is the coating of thepolyvinyl alcohol resin treated mat with another coating to obtainimproved release in regions of the mat such as sharp crevices and sharpcorners of the different letters.

Other objects of the invention will become apparent from the descriptionwhich follows.

In fulfillment of the above and other objects, this invention provides aprocess of preparing a stereotype mat comprising mixing a properlyplasticized polyvinyl alcohol and water, placing the mixture upon themolding and casting surface of a stereotype mat, and then spreading themixture uniformly across said molding and casting surface to form auniform layer of polyvinyl alcohol, said layer containing from about .5to about 5 pounds of polyvinyl alcohol per 1,000 square feet of saidmolding and casting surface. Preferably, the water is removed from saidmixture both by absorption into the mat and by evaporation.

In order to obtain a matrix mat of reduced pick-out characteristics thepolyvinyl alcohol used must be plasticized with the followingplasticizers: glycerine, ethylene glycol, p,p-dihydroxy diethyl ether,1-3 butane diol, or the like. The preferred plasticizer is 1-3 butanediol.

Acceptable properties are obtained when 12.5 parts by weight ofplasticizer are used per parts by weight of polyvinyl alcohol in theform of glycerine. Preferred results are obtained when both glycerineand 1-3 butane diol are used as plasticizers. When these plasticizersare mixed with 2 parts by weight glycerine and 1 part by weight l-3butane diol and 12 /2 parts by weight of this mixture is used per 100parts by weight of polyvinyl alcohol, the results are much improved overthe use of glycerine alone.

In order to further improve the release of the cast resin platesespecially in the sharp crevices and corners which may expose loosecellulose fibers an additional coating agent is used. This agent is soldunder the trademark Zonyl RP by the Du Pont Chemical Company,Wilmington, Delaware, and reputedly has the chemical description of apolyfluoroalkyl phosphate. Physical properties of Zonyl RP are given inTable I below.

TABLE I. PHYSICAL PROPERTIES OF ZONYL RP Unaffected (Zonyl RP should Tofreezing be stirred after thawing). To pH changes Unaffected, pH 7.0 andup.

The amount of Zonyl RP used is of from .5 pound to 3.0 pounds per 1,000square feet of mat surface. A preferred amount is 1 pound 3 ounces per1,000 square feet of mat surface.

As a consequence of the above treatments a properly prepared matrix matgixes improved properties such as no pick-out of fibers.

In practicing the process of the present invention, the steretoype matused preferably includes co-felted cellulose fibers and discreteparticles of a filler. The above described spreading operation, wherebythe polyvinyl alcohol solution is applied to the mat, is accomplishedpreferably by means of oscillating brushes in order that the polyvinylalcohol mixture not only coats the complete surface of the face, butalso penetrates into interstices of the mat. A. suitable oscillatingbrush arrangement for the present purpose might comprise a coatingapparatus manufactured by the John Waldron Corporation of New Brunswick,N; 1., Model 1459A. After application of the liquid polyvinyl alcoholmixture, a substantial portion of 'the water is removed therefrom byabsorption into the mat and evaporation.

The Zonyl RP solution must be sprayed on the face of the mat,'that -is,over the surface coated by the plasticized polyvinyl alcohol. Thisspraying is preferably done by airless spray equipment manufactured byAlemite Sales Company, Inc., of Indianapolis, Ind. The Zonyl RP asdescribed in Table I is diluted before spraying in the followingproportions: 1 part by weight Zonyl to 2.3 parts by weight water. Thismixture is then sprayed on the mat so as to apply about 1 pound 3 ouncesof Zonyl RP (as described in Table I) per 1,000 square feet of matsurface.

In one preferred embodiment of the invention, the gly cerine plasticizerwas added at a proportion of one part by weight of glycerine to eightparts by weight of polyvinyl alcohol (4% ,by'w'eight in water).

, least 4%.

Example No.1

An aqueous slurry of coniferous alpha pulp fibers is placed in a beaterand beaten until the fibers are well separated and there is suitablehydration thereof. A suitable amount of a filler, in this caseapproximately 30% of powdered silicate, based on the oven dry weight ofthe fibers, is added to the slurry, and the mass agitated until athorough, initimate mixture of fiber and filler is obtained. The slurryis then transferred to a wet machine and the mixture of fiber and filleris felted out on the screen in the form of a web and the web transferredto a roll upon which it is wound until a sheet of the desired thicknessis obtained. The sheet is then removed from the roll and dried andcompressed to the desired thickness, usually between 0.26 and .070 inch,for example, .068 inch. The compression and drying are carrier out witha porous woven fabric sheet against the back of the mat and with acalendering roll operating across the face of the mat, whereby the faceis compressed to a relatively dense, smooth, uniform surface, while theback is relatively porous and irregular.

A coating is then applied to the calendered face of the stereotype matof the following composition:

10 lbs. polyvinyl alcohol 30 gallons of water The polyvinyl alcohol isadded to the water and the resulting liquid composition is thoroughlymixed and heated to 180200 F. to provide a fluid liquid.

The composition is applied to the face of the mat by the coatingapparatus mentioned above which applies a uniform coating over thesurface of the mat. The compotion is applied to the mat in an amountproviding one pound of polyvinyl alcohol for each 1,000 square feet ofsurface of the mat. The mat is then moved beneath the above mentionedoscillating brush arrangement whereby the composition is caused topenetrate into the mat. The water in the composition is caused toevaporate and to be absorbed into the mat. The mat is then re-wet bysuitable spraying apparatus until it contains 18% water based on the dryweight of the mat.

The mat is then subjected to the usual molding procedure in'which aprinting form containing type and/or illustration is impressed againstthe face of the mat. The mat takes a deep and sharply defined impressionof the form. The mat is then dried in a scorcher and placed in in a acasting box. A thermoplastic resin is cast against the mat according toconventional casting procedure. An exact reproduction of the form ismade and the cast plate separates from the stereotype mat with anexcessive tendency to adhere. This is demonstrated by the discolorationwhich the resin causes when it penetrates into the face of the mat.

Throughout the specification, the term polyvinyl alcohol is meant toinclude a material prepared by hydrolysis of polyvinyl acetate having asolubility in water of at In general, at least 35% of the acetate groupsmust be hydrolysed from polyvinyl acetate to yield a polyvinyl alcoholhaving the desired solubility in water. I prefer to use, however, apolyvinyl alcohol which still retains about 5% or so of the originalacetate groups, although any polyvinyl alcohol having from about 1 to 5percent residual acetate groups is fully operative.

Example N0. 2

A stereotype mat is formed in the manner described above in connectionwith Example No. 1 up to and including the drying and compressing of themat by a calendering operation to bring the mat to the desiredthickness. A coating is then applied to the calendered face of thestereotype mat, said coating including 10 pounds of polyvinyl alcoholmixture and 30 gallons of water. The polyvinyl alcohol mixture is addedto the water in the same manner described above with relation to ExampleNo. 1 and the resulting liquid composition is thoroughly mixed andheated to 180-200 F. to provide a fluid liquid.

The polyvinyl alcohol mixture of the present example includes 8 parts byweight of dry Vinol 165 and 1 part by Weight of a mixture includingglycerine and 1-3 butane diol at a two to one ratio by weight. Vinol 165is a polyvinyl alcohol dry powdered product of the Airco ChemicalCompany, 150 E. 42nd St., New York, N.Y. Vinol 165 is further identifiedby the fact that it has a viscosity of 55-65 cps., a percent hydrolysisof 997+, a percent volatiles max. of 5.0, a max. ash percentage of 1.0,and a pH of 6-8. In the present example, the compositon is placed uponthe face of the mat in an amount providing one pound of polyvinylalcohol for each 1,000 square feet of surface of the mat. The polyvinylalcohol is applied to the mat by the use of the above describedoscillating brush arrangement. After the water in the compositionevaporates and is absorbed .into the mat, the mat is re-wet by suitablespraying apparatus until it contains water based on the dry weight ofthe 'mat. It will be noted that the above mentioned glycerine and butanediol provide plasticizing action. The use of the above two-componentplasticizer makes possible reasonably effective casting and release ofliquid thermoplastic resin.

Example N 0. 3

The stereotype mat is formed and treated in exactly the same mannerdescribed above in Example No. 2 with the exception that the polyvinylalcohol mixture consisting of glycerine and of 1-3 butane diol in a 2 to1 weight ratio is applied to the mat surface in the amount of 2 poundsof polyvinyl alcohol per 1,000 square feet. The resulting mat exhibitsthe same excellent molding but does show improved release over ExampleNo. 2 when casting liquid thermoplastic resin thus demonstrating thatthe quantity of coating mixture per 1,000 square feet of mat surface isof prime importance.

Example N0. 4

This example is identical to Example No. 3 except that 5 pounds ofpolyvinyl alcohol per 1,000 square feet were applied instead of 2 poundsper 1,000 square feet. No appreciable improvement in release iseffected.

Example N0. 5

The stereotype mat is formed an-d treated in exactly the same mannerdescribed above in Example No. 3. The polyvinyl alcohol and plasticizedmixture is applied as above described. The coating is dried byabsorption and external infra-red heat. It is then passed through aspraying tunnel where the Zonyl RP is sprayed on the coated side of themat over the polyvinyl alcohol coating. The Zonyl RP (as described inTable I) is prepared for spraying by dilution with water in the amountof 1 part Zonyl to 2.3 parts of water. The speed of the mat through thespraying tunnel and the volume of Zonyl sprayed must be controlled so asto apply about 1 pound 3 ounces of Zonyl RP (as described in Table I)per 1,000 square feet of mat surface. The diluted Zonyl and the watermixture is then caused to dry by absorption and external heat and themat then re-wet to 15 to 18% water based on the 'dry weight of the mat.It is then molded and cast in exactly the same way as described inpreceding examples. The resulting mat readily separates from the castplate and exhibits excellent release properties. The method ofproduction described in this example is the present commercial methodused by applicants assignee.

Example N0. 6

The stereotype mat is formed and treated in exactly the same mannerdescribed above in connection with Example No. 3 with the exception thatthe polyvinyl alcohol mixture in dry powdered form consisted of 8 partsby weight dry Vinol 350 plus a plasticizer mixture consisting of 1 partby weight of glycerine and of 1-3 butane diol in a 2 to 1 weight ratio.The resulting mat exhibits the same molding and release properties whencasting liquid thermoplastic resin as does the mat of Example No. 3.Vinol 350, also a product of Airco Chemical Company, is a polyvinylalcohol in dry powdered form having a viscosity of 55-65 cps., a percenthydrolysis of 98.0-98.8, a percent max. volatiles of 5.0, a percent ashof 1.0 and a pH of 6-8.

Further examples The following further examples of the invention werecarried out in exactly the same fashion as Example No. 3 with theexception that the polyvinyl alcohol was applied to an extent providing2 pounds of alcohol for each 1,000 square feet of surface and the waterin the solution is caused to evaporate and to be absorbed in the mat.Also the mats are re-wet until the mat contained 15 water based on thedry weight of the mat.

Example N0. 7.Vinol 165 plus glycerine (8 parts by weight of drypolyvinyl alcohol to 1 part by weight glycerine) Example N0. 8.-Vinol350 plus glycerine (8 parts 'by weight of dry polyvinyl alcohol to 1part by weight glycerine) Example N0. 9.Vinol plus glycerine (8 parts byweight of dry polyvinyl alcohol to 1 part by weight glycerine) ExampleN0. 10.-Vinol plus 1-3 butane diol (8 parts by weight dry polyvinylalcohol to 1 part by weight of 1-3 butane diol) Example N0. 11.Vinol 350plus 1-3 butane diol (8 parts by weight dry polyvinyl alcohol to 1 partby weight of 1-3 butane diol) Example No. 12.-Vinol 125 plus 1-3 butanediol (8 parts by weight dry polyvinyl alcohol to 1 part by weight of 1-3butane diol) Each of the above Examples 7-12 produced mats whichexhibited excellent molding and release prope'rties which propertieswhen complemented with the Zonyl RP treatment produce resin plates ofsuperior properties.

While the invention has been disclosed and described in some detail inthe foregoing description, the same is to be considered illustrative andnot restrictive in character, it being understood that only preferredembodiments have been described and that all changes and modificationsthat come within the spirit of the invention and scope of the claims arealso desired to be protected.

The invention claimed is:

1. A process of preparing a stereotype mat for use in the casting ofresin printing plates which comprises mixing polyvinyl alcohol,plasticizer and water, said polyvinyl alcohol containing no more than 5%residual acetate groups, placing said mixture upon the molding andcasting surface of a stereotype mat, and spreading said mixtureuniformly across said surface to form a uniform layer of between .5 and5 pounds of polyvinyl alcohol per 1,000 square feet of said molding andcasting surface, and removing a portion of the water from said polyvinylalcohol by absorption into said mat; and further treating the surface ofsaid mat with a release improving agent, said release improving agentbeing a polyfiuoroalkyl phosphate, said polyfiuoroalkyl phosphate beingcharacterized as a clear, light brown liquid having an alcoholic odor,33% solids, a density of 8.85 lbs./ gal. at 77 F., a viscosity of 10cps. at 77 .F., a flash point, Tag Open Cup, of 105 F, a pH of 7.0, saidpolyfiuoroalkyl phosphate being soluble in water in all proportions,slightly soluble in polar solvents and having negligible solubility innon-polar solvents, said polyfiuoroalkyl phosphate being unaffected byaging, freezing and pH changes of 7.0 and up.

2. A process according to claim 1 wherein the surface of said mat istreated with said polyfiuoroalkyl phosphate by depositing on the matfrom about .5 pound to 3.0 pounds of said polyfluoroalkyl phosphate per1,000 square feet of said surface.

3. A process according to claim 2 wherein said polyfiuoroal-kylphosphate is sprayed onto the surface of said mat.

4. A process according to claim 2 wherein said surface of said mat istreated with said polyfluoroalkyl phosphate by depositing on the matlpound 3 ounces of said polyfluoroalkyl phosphate per 1,000 square feetof mat surface.

5. A stereotype mat comprising co-felted cellulose fibers and discreteparticles of a filler, said mat having present at the molding andcasting surface thereof a uniform coating of plasticized polyvinylalcohol, said polyvinyl alcohol containing no more than 5% residualacetate groups, said polyvinyl alcohol coating carrying on its surfacefromabout .5 to about 3 pounds per 1,000 square feet of mat'surface of arelease improving agent, said release improving agent being apolyfluoroalkyl phosphate characterized as a clear, light brown liquidhaving an alcoholic od-or, 33% solids, a density of 8.85 lbs./ gal. at77 F., a viscosity of 10 cps. at 77 F., a flash point,

Tag Open Cup, of 105 F., 'a pH of 7.0, said poly-fluoroalkyl phosphatebeing soluble in water in all proportions, slightly soluble in polarsolvents and having negligible solubility in nonpola'r solvents, saidpolyfiuoroalkyl phosphate being unaffected by aging, freezing and pHchanges of 7.0 and up.

References Cited by the Examiner OTHER REFERENCES Handbook of Plastics,2nd edition, New York, D. Van Nostrand Company, Incorporated, 1949,pages 569, 570, 724, and 725.

ROBERT E. PUIJFREY, Primary Examiner.

L A. BELL, Assistant Examiner.

5. A STEREOTYPE MAT COMPRISING CO-FELTED CELLULOSE FIBERS AND DISCRETEPARTICLES OF A FILLER, SAID MAT HAVING PRESENT AT THE MOLDING ANDCASTING SURFACE THEREOF A UNIFORM COATING OF PLASTICIZED POLYVINYLALCOHOL, SAID POLYVINYL ALCOHOL CONTAINING NO MORE THAN 5% RESIDUALACETATE GROUPS, SAID POLYVINYL ALCOHOL COATING CARRYING ON ITS SURFACEFROM ABOUT .5 TO ABOUT 3 POUNDS PER 1,000 SQUARE FEET OF MAT SURFACE OFA RELEASE IMPROVING AGENT, SAID RELEASE IMPROVING AGENT BEING APOLYFLUOROALKYL PHOSPHATE CHARACTERIZED AS A CLEAR, LIGHT BROWN LIQUIDHAVING AN ALCOHOLIC ODOR, 33% SOLIDS, A DENSITY OF 8.85 LBS./GAL. AT77*F., A VISCOSITY OF 10 CPS. AT 77*F., A FLASH POINT, TAG OPEN CUP, OF105*F., A PH OF 7.0, SAID POLYFLUOROALKYL PHOSPHATE BEING SOLUBLE INWATER IN ALL PROPORTIONS, SLIGHTLY SOLUBLE IN POLAR SOLVENTS AND HAVINGNEGLIGIBLE SOLUBILITY IN NON-POLAR SOLVENTS, SAID POLYFLUOROALKYLPHOSPHATE BEING UNAFFECTED BY AGING, FREEZING AND PH CHANGES OF 7.0 ANDUP.